Vol. 57.] AMONG THE MALVERN CAMBRIANS. 159 



generally appears to range from 51 to 58 ; the specific gravity, 

 so far as determined, ranges usually from 258 to 2-67. 



Some of the best-preserved examples are seen in the HoUybush 

 Sandstone ; the intrusions in this rock appear as dykes and small 

 bosses. The distribution of those is shown in fig. 1 of the writer's 

 paper on the Southern Malverns.^ At the south-western corner of 

 Midsummer Hill the presence of a number of small intrusive masses 

 gives the grouud a somewhat huramocky character. The relation of 

 the dyke (M 112) to the Sandstone is shown in fig. 9 (p. 140) of the 

 paper just quoted. At the north-western corner of Uaggedstone 

 Hill the main road cuts through another dyke of greater length, 

 though it hardly extends so fai* as Holl stated.^ Near its southern 

 end is a small boss, and a portion of a second dyke : both of these 

 would seem to invade not only the Hollybush Sandstone but also 

 the Quartzite.^ The Sandstone frequently seems to be much 

 indurated and darkened in the neighbourhood of the long dyke, as 

 Phillips evidently perceived."* This dyke is probably about 90 feet 

 thick. 



The material of these small intrusives is very uniform. It is 

 compact, varies in colour from reddi>h-grey to dark greyish-blue, 

 and shows small black-green pherocrysts. It weathers to a reddish 

 or dark greenish-brown. The rock exposed is ns a rule badly pre- 

 served, but sounder examples may be obtained here and there. 



Under the microscope the freshest specimens (M 112 & M 439a) 

 show a reddish, fine-grained pilotaxitic (or hyaloi)i]itic) groundmass 

 (PL VII, fig. 6, and text-fig. 2, p. 161), consisting laigely of small, 

 turbid, mostly untwinned laths of felspar (an desine) showing flow- 

 structure ; numerous granules of augite ; much scattered ilmenite 

 and titaniferous magnetite; a little apatite, as well as pale 

 serpentine, titanite, pyrites, and other products of decom- 

 position. The serpentine occurs in small irregular patches; 

 but, owing to the altered condition of the rock, it is impossible to 

 determine its source. Glass may have been present originally, but 

 it is questionable whether any traces of it exist (see p. 161). 



The ])heuocrysts include small reddish felspars, both simple and 

 twinned; small pale augites; long or short needles, and short 

 stout prisms of amphibolc; to these may be added ragged plates 

 of ilmenite, which appear to bo original constituents. No traces 

 of quartz, olivine, rhombic pyroxene, or of other phenocrysts can be 

 detected. 



Sections of other rocks (M160rt & M 243) intrusive in the 

 Sandstone show an essentially similar constitution, but they are 

 still more weathered, and the substance of the phenocrysts is often 

 decomposed to such an extent that these are barely distinguishable 



' Quart. Journ. Geol. Soe. vol. Iv (1899) p. 132. 

 , 2 iind. vol. xxi (1865) p. 88. ^ //.^-^ ^^,] i^ (jsqc)) fjg, j^ p^ 132. 



" Mem. Geol. Suit .Gt. Brit. vol. ii, pt. i (1848) p. 53, 



